New guidance from the Energy Department would prevent people from receiving rebates after making such swaps.

© Bing Guan for The New York Times

Companies say it’s a better way to dispose of the Cold War-era material — and fix a shortage of nuclear fuel. But the plan has also faced criticism from nonproliferation experts.

© Science Source

The dream of clean hydrogen has tantalized energy experts for years, but producing it has been tough. Many start-ups think the answer could lie beneath our feet.

A new wave of start-ups are trying to harvest emissions-free energy from inside the Earth, but the industry still faces significant challenges.

© Eduardo Munoz/Reuters